Studies are conducted in patients with medically intractable partial epilepsies to improve the diagnosis and the surgical treatment. Improved localization of seizure foci is achieved by the use of arrays of stereotactically implanted intracerebral electrodes, long term telemetric monitoring during all types of behavior including seizures and videotape recordings of the attacks. Approximately 3/4 of patients show a consistently localized focus during repeated attacks. We are studying neuropsychological aspects of epileptic patients associated with seizures, with brain damage and after cortical resections for treatment. The pathophysiology of the partial epilepsies is studied by means of indwelling microelectrodes recording extracellular, multiple unit activity for up to a week in the amygdala and hippocampal formation. Different stages of epileptogenesis of neurons in the deep temporal lobe have been correlated with simultaneous recordings of neuronal firing and EEG patterns. A comparison of surface and EEG changes by three computer systems is under study to determine if depth spiking can be detected from surface recordings. The EEG patterns of propagation from depth to surface have been documented in 34 patients. Pathological alterations in epileptogenic cortical regions have been studied by Golgi preparations and electron microscopy. Intravenous diazepam has been studied for its effects on interictal EEG, suppression of discharges within and outside the focus and as an aid to localization. BIBLIOGRAPHIC REFERENCES: Babb, T.L. and Crandall, P.H. Epileptogenesis of human limbic neurons in psychomotor epileptics. Electroenceph. clin. Neurophysiol. 40: 225-243, 1976. Dymond, A.M. and Crandall, P.H. Oxygen availability and blood flow in the temporal lobes during spontaneous epileptic seizures in man. Brain Research 102:191-196, 1976.